What is the effect of increasing carbon dioxide concentration on the rate of photosynthesis?

The rate rises, because more carbon dioxide is available as a reactant, until another factor holds it back.

Why does raising the temperature towards the optimum increase the rate of photosynthesis?

The enzymes controlling the reaction work faster as the molecules move more quickly.

Why does the rate of photosynthesis fall sharply at very high temperatures?

The enzymes controlling the reaction are denatured, so it slows down and stops.

Why is a greenhouse often heated and lit in winter?

Raising both temperature and light intensity increases the rate of photosynthesis, so the crop grows faster.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

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Global Challenges

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Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Cell Level Systems

Limiting factors in photosynthesis

3 things to know
Paper 7 (Biology)

Overview

How light intensity, carbon dioxide concentration and temperature each change the rate of photosynthesis, what a limiting factor is, reading graphs of rate against light, and heating and lighting a greenhouse.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is photosynthesis slow on a bright, cold day, what is a limiting factor, and what does a levelled-off graph of rate against light show?

Key term

What happens to the rate of photosynthesis as light intensity is increased from darkness?

Key term

Why does the rate of photosynthesis stop rising at very high light intensity?

Questions from this subtopic

Each one with the model answer underneath.

1
What happens to the rate of photosynthesis as light intensity is increased from darkness?
Model answer
The rate increases, because more light energy is available to drive the reaction.
2
Why does the rate of photosynthesis stop rising at very high light intensity?
Model answer
Something else, such as the temperature or the carbon dioxide supply, is then holding the rate back.
3
What is the effect of increasing carbon dioxide concentration on the rate of photosynthesis?
Model answer
The rate rises, because more carbon dioxide is available as a reactant, until another factor holds it back.
4
Why does raising the temperature towards the optimum increase the rate of photosynthesis?
Model answer
The enzymes controlling the reaction work faster as the molecules move more quickly.
5
Why does the rate of photosynthesis fall sharply at very high temperatures?
Model answer
The enzymes controlling the reaction are denatured, so it slows down and stops.
6
Why is a greenhouse often heated and lit in winter?
Model answer
Raising both temperature and light intensity increases the rate of photosynthesis, so the crop grows faster.

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Genes, Inheritance and Selection

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